Field of the Invention
The present disclosure relates to an organic light emitting display device and a method of manufacturing the same, and more particularly, to an organic light emitting display device including a pad electrode structure improved in reliability and a method of manufacturing the same.
Description of the Related Art
An organic light emitting display device (OLED) is a self-light emitting display that does not need a separate light source as in a liquid crystal display device, and, thus, the organic light emitting display device can be manufactured into a lightweight and thin form. Further, the organic light emitting display device is advantageous in terms of power consumption since it is driven with a low voltage. Also, the organic light emitting display device has excellent color expression ability, a high response speed, a wide viewing angle, and a high contrast ratio (CR). Therefore, the organic light emitting display device has been receiving attention as a next-generation display device.
Organic light emitting display devices are categorized into a top-emission organic light emitting display device, a bottom-emission organic light emitting display device, and a dual-emission organic light emitting display device according to an emission direction of light.
In a top-emission organic light emitting display device, an anode may be formed of a conductive material having an excellent reflection and a proper work function. However, there is no existing single material satisfying such characteristics. Therefore, the anode in the top-emission organic light emitting display device is formed into a multi-layer structure including conductive layers, and may be formed into a structure in which, for example, an ITO (Indium Tin Oxide) layer, a silver alloy (Ag alloy) layer, and an ITO layer are laminated. Accordingly, a light emitted from an organic light emitting layer of an organic light emitting element is reflected at the Ag alloy layer, so that a top-emission organic light emitting display device is realized.
Meanwhile, a pad electrode in a general organic light emitting display device is bonded to an external module and configured to receive an electrical signal from the external module or output an electrical signal to the external module. An uppermost layer of a pad electrode in a general top-emission organic light emitting display device is formed of the same material as an anode. To be specific, the pad electrode is formed of the same material as the anode on an electrode formed of the same material as a source electrode and a drain electrode of a thin film transistor.
Herein, a layer formed of the same material as the anode, i.e., the uppermost layer of the pad electrode, is formed at the same time when the anode is formed. To be specific, the anode and the uppermost layer of the pad electrode are formed by performing an etching process in a state where an ITO material, an Ag alloy material, and an ITO material are laminated. Therefore, the uppermost layer of the pad electrode is also formed into a structure in which an ITO layer, an Ag alloy layer, and an ITO layer are laminated and a lateral side (surface) of the Ag alloy is exposed to the outside. When the Ag alloy layer with the exposed lateral side is damaged, a driving defect of the organic light emitting display device may be generated.
To be specific, in order to test reliability of the organic light emitting display device, a panel on which organic light emitting elements are formed is kept in a high-temperature chamber for a certain period of time. In this case, the Ag alloy layer of the pad electrode may be damaged due to a high temperature in the chamber, so that the pad electrode cannot be brought into contact with the external module and the organic light emitting display device may not be normally operated, thereby causing a driving defect.
Further, when the Ag alloy layer of the pad electrode is exposed to the outside, the Ag alloy layer may react with water (moisture) and air. In this case, a galvanic effect is generated between the Ag alloy layer and the ITO layer. A galvanic effect refers to a phenomenon occurring when two materials different in electromotive force (EMF) are exposed to a corrosive solution at the same time. A material having a high EMF is corroded, so that the pad electrode has an insulating property. Therefore, there may be generated a driving defect in which the pad electrode is not brought into contact with the external module and the organic light emitting display device is not normally operated.
Further, during a module process (or similar manufacturing procedure), the pad electrode may be in a high-temperature and high-pressure condition. In such a high-temperature and high-pressure condition, if water (moisture) is applied to the lateral side of the Ag alloy layer exposed to the outside, migration occurs in the Ag alloy layer. Therefore, a part of the Ag alloy layer increases, so that there may be generated a driving defect in which adjacent pad electrodes are shorted and the organic light emitting display device is not normally operated.
Accordingly, a method has been considered to form pad electrode only of the same material as the source electrode and the drain electrode without using the layer formed of the same material as the anode, i.e., the uppermost layer of the pad electrode. However, metal materials generally used for the source electrode and the drain electrode may be washed away by an etchant used in an etching process for forming the anode.